The invention relates especially to wear components employed in plants for grinding, crushing and conveying various abrasive materials which are encountered in industries such as cement factories, mines, metallurgy, electricity generating stations or various quarries. These components are often subjected to high mechanical stresses in the bulk and to a high wear by abrasion at the working face. It is therefore desirable that these components should exhibit a high abrasion resistance and some ductility, to be able to withstand the mechanical stresses such as impacts and to be capable optionally of being mechanical.
Given that these two properties are difficult to reconcile with one another in the same material, composite components have already been proposed which have a core made of relatively ductile alloy in which isolated inserts which have a good wear resistance are embedded.
Document EP-A-0476496 proposes this technique for the production of grinding wheels whose working face has set-in inserts made of chrome pig iron.
Since it is known that ceramic materials have good abrasion resistance properties, it is also known to employ these materials for improving the abrasion resistance of wear components.
Document EP-A-0575685 proposes the use of ceramic materials in a moulding by lost-wax precision casting of small wear components.
This well-known process employs wax models which must be melted to obtain the mould cavity which must be filled with metal; this mould itself is made of ceramic and not of a conventional sand.
According to this document a ceramic pad (wafer core) is formed first, with a spongy structure which has a three-dimensional network of open pores all of which communicate with one another. This ceramic pad is formed by pouring grains of ceramic materials into an appropriate mould and, next, a liquid adhesive with a good fluidity, for example a liquid resin which, after curing, retains the grains to form the ceramic structure. The ceramic material may consist of aluminium oxide or of zirconium oxide. After having been pre-impregnated with wax, this pad is placed in a mould intended to produce the wax model of the component. The wax model is then case and, lastly, the ceramic mould is produced by dipping the wax model in a ceramic slurry. The ceramic mould containing the wax model is then heated so as to melt the wax model. The wax thus flows from the ceramic mould but the pads inserted beforehand in the wax model remain adhesively bonded to the walls of the ceramic mould.
For the casting of metal in the ceramic mould the latter is preheated to a temperature of the order of 1150° C., generally under vacuum.
This known technique is limited, however, to lost-wax precision moulding. Moreover, the compatibility between the metal matrix and the ceramic structure, especially in terms of temperature behaviour, presents hardly any problems in the case of the applications mentioned in this document, given that, when the metal is being cast, the mould and the ceramic structure are preheated to a high temperature. In addition, the technique is limited to the production of very precise special components, which are sold at a very high price because the lost-wax moulding process itself is very costly.
The document “Ullmann's Encyclopedia of Industrial Chemistry” (1985), W. Gerhartz, VCH Verslagsgesellschaft, 5th Edition XP002023826, page 5 mentions compositions based on Al2O3—ZrO2 for grinding devices intended for conditioning cast products (billets and slabs).